1. Field of the Invention
The invention relates generally to heat exchangers and more particularly to a thin flexible heat exchange panel for transferring heat to or from a complex shape such as a portion of a human body.
2. Description of the Prior Art
Compliant heat exchange panels are used for cooling a portion of a human body for physical therapy, pre-game day conditioning, minor injury care, post orthoscopic surgery recovery, and as a replacement for general air-conditioning. The heat exchange panels operate by transferring heat from the human body to a heat absorbing medium having a lower temperature than the body. The heat exchange panel may be passive where the medium is stationary within the panel or active where the medium, typically a liquid, flows through the panel. A common example of a passive heat exchange panel is an ice pack. A limitation of a passive heat exchange panel is that the panel or the medium must be changed when the temperature of the medium rises. An active heat exchange system is more expensive because an external apparatus is required to pump and re-cool the liquid. However, an active heat exchange system is preferable for many applications because it can operate continuously over a long period of time while maintaining a constant controllable temperature.
In order to achieve the best results in an active heat exchange panel, the flowing liquid at every point within the panel must have a nearly constant temperature and the panel must be flexible in order to conform to the various complex shapes of the human body for thermal contact. These requirements are easier to meet when the heat exchange panel is very thin.
FIGS. 1A and 1B are cross-sectional and plan diagrams, respectively, of a heat exchange panel of the prior art referred to by a reference number 100 and disclosed by William Elkins in U.S. Pat. Nos. 4,884,304 and 5,033,136 for a “Bedding System With Selective Heating and Cooling”. Similar heat exchange panels are disclosed by Elkins in U.S. Pat. Nos. 3,830,676 for a “Process of Making a Controlled Thermal Device” and U.S. Pat. No. 4,691,762 for a “Personal Temperature Control System”. The heat exchange panel 100 includes a first layer 102 and a second layer 104. The first layer 102 and the second layer 104 are sealed together at a common border 106 and at fences 108. A liquid 120 is pumped so that it flows into an inlet port 122, through channels 124 between the fences 108, and out of an outlet port 126. The pressure of the liquid 120 causes the channels 124 to bulge to a certain thickness that depends upon the spacing of the fences 108. The panel 100 makes external thermal contact at the bulges over the channels 124. The fences 108 should be spaced as close together as possible in order for the panel 100 to be as thin as possible. However, spacing the fences 108 closer together requires an increase in the number of fences 108 and thereby reduces the area of the channels 124 where the panel 100 can make thermal contact.
In the heat exchange panel 100, the border 106 and the fences 108 are straight and essentially without wrinkles or ripples. Unfortunately, the straight border 106 and fences 108 cause the panel 100 to buckle when it is expanded with the liquid 120. The buckling impedes the flow of the liquid 120 and prevents the panel 100 from conforming closely to complex shapes. Elastic material could be used to alleviate these problems, however, the dimensions of elastic materials are more difficult to control.
FIG. 2A is a plan diagram of a heat exchange panel referred to by a reference number 200 that was developed in part to improve upon the heat exchange panel 100. The heat exchange panel 200 includes a first layer that is similar to the first layer 102 (FIG. 1A) and a second layer similar to the second layer 104 (FIG. 1A). The first layer and second layers of the panel 200 are sealed together at a common border 206, at fences 208, and at dots of a dot matrix 210. The dot matrix 210 is organized into first imaginary parallel lines L12, second parallel lines 213, and third parallel lines 214 for connecting each of the dots to the nearest adjacent dots of the dot matrix 210. The lines 212–14 cross each other at angles of approximately 60°. A typical section 215 of the panel 200 is expanded in FIG. 2B. The FIG. 2B shows each of the dots in the dot pattern. Each is at the center of an arc of six nearest adjacent dots. The six adjacent dots form a hexagonal pattern 216. Groups of four dots consisting of the center dot and a contiguous three of the nearest adjacent dots form a parallelogram 217. The liquid 120 is pumped to flow into an inlet port 222, between the fences 208, in a nominal direction 225 through the dot matrix 210, and out of an outlet port 226.
The pressure of the liquid 120 causes the channels 224 to bulge between the dots of the dot matrix 210 to a certain thickness that depends upon the spacing of the dots. The panel 200 makes external thermal contact at these bulges. The dots of the dot matrix 210 should be spaced as close together as possible in order for the panel 200 to be as thin as possible for conforming to complex shapes of various portions of the human body and avoiding warm spots due to relative stagnation of the liquid flow. However, increasing the number of dots of the dot matrix 210 reduces the area of the bulges where the panel 200 can make thermal contact. Consequently, it is important to space the dots of the dot matrix 210 as close together as possible while using a minimum number of dots. Unfortunately, while an improvement over the panel 100, the heat exchange panel 200 having the dot matrix 210 having the lines 212–14 crossing at angles of 600 with the hexagonal pattern 216 is not optimum in this respect.
The panel 200 differs from the panel 100 by having trapezoid and triangular shaped wrinkles in the border 206 and the fences 208. The wrinkles reduce the tendency to buckle when the panel 200 is inflated and enable the panel 200 to conform better to complex shapes as compared to the panel 100. However, the hard or, in other words, adrupt corners of the wrinkles decrease the laminar flow of the liquid 120 enabling thermal zones of warmer liquid to form, thereby reducing the performance of the heat exchange panel 200.